1. Field of the Invention
The present invention generally relates to a method and apparatus for fluid level regulation in a media coating system. More particularly, the present invention relates to a method and apparatus for sensing and regulating liquid ink and coating levels in an inkjet printing system and maintaining the satisfactory operation thereof.
2. Background Art
Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge nozzle. A plurality of chambers, each provided with a single heating element, are provided in the printer's print head. The print head typically comprises the heater chip and a nozzle plate having a plurality of the discharge nozzles formed therein. The print head forms part of an ink jet print cartridge that also comprises an ink-filled container.
Ink jet printers have typically suffered from two major shortcomings. First, optical density of a printed image varies greatly with the print media or substrate being printed upon. Second, ink drying time is excessive on some media types.
Interaction between the ink and print media or substrate influences the performance of the ink jet printer. Different media types behave differently with the ink and not all media types are well suited for ink jet printing. Accordingly, attempts have been made to apply a liquid coating to the media before printing that interacts with the ink to improve the quality of the resulting printed image. The ink may contain, for example, penetrants to improve dry time and binders to improve performance. These “pre-coating” liquids may contain materials that cause the ink to flocculate on the surface of the media, improving image quality. Pre-coating liquids have previously been applied to the print media using a separate ink jet print head and by the use of a roll coating apparatus that directly contacts the print media prior to ink application. One roll coating apparatus and method of the prior art is shown and described in U.S. Pat. No. 6,183,079, assigned to Lexmark International, Inc.
Thus, a primary function of the media coating device is to deliver a uniform coat of specialized fluid to the print medium prior to printing. As the media is printed on, the interaction of the fluid and the ink results in superior optical density and faster dry time. As this specialized fluid is delivered to the coating device through a supply item, it becomes necessary to detect the presence of the supply item, and detect, maintain and control the level of the fluid within the coating device for it to perform properly. In particular, when the specialized fluid in the device's reservoir is depleted, timely refill should be conducted. In doing so, overfill should be avoided, and normal printing processes should not be interrupted.
Accordingly, there is a need for an apparatus for fluid level management in a media coating system for an inkjet printer that is capable of detecting, maintaining, filling and controlling the level of the specialized fluid in the media coating system.